Effects of Surface Roughness on Turbulent Boundary Layers
Abstract
Direct numerical simulation of turbulent channel flow between a smooth wall and one covered with three-dimensional roughness elements is performed to study the effects of surface roughness on turbulent boundary layers. While the impact of roughness upon the mean-velocity profile of turbulent wall layers is well understood, the manner in which other features are affected, especially in the outer layer, has been more controversial. Our results show that both statistics and turbulence structures in the outer layer are significantly affected by the presence of surface roughness. The higher-order moments and the energy budgets demonstrate significant differences between the smooth and rough sides in the wall-normal flux of the Reynolds shear stresses and turbulence kinetic energy. The length scales and flow dynamics in the roughness sublayer, the spatially inhomogeneous layer within which the flow is directly influenced by the individual roughness elements, are also examined. Our goal is to classify the effects of surface roughness in terms the following input parameters, such as roughness distribution and aspect ratio of the roughness elements in the streamwise and spanwise directions, and how these parameters affect the roughness length scales including the roughness sublayer. Possible alternative (non-smooth wall) mechanisms involved in producing and maintaining near-wall turbulence in rough-wall boundary layers are also examined.
- Publication:
-
APS Division of Fluid Dynamics Meeting Abstracts
- Pub Date:
- November 2003
- Bibcode:
- 2003APS..DFD.EA005B